BOSTON - Massachusetts prison officials have identified six doctors willing to perform a sex-change operation on a convicted murderer, but none practices in the state.

A federal judge ruled in September that sex reassignment surgery is the "only adequate treatment" for Michelle Kosilek's gender-identity disorder. The state has appealed.

According to an affidavit filed by state Correction Commissioner Luis Spencer made public Tuesday, there are no doctors in Massachusetts who regularly perform the surgery. Spencer wrote that having identified potential surgeons, planning will now focus on getting permission for the out-of-state doctors to work in Massachusetts and choosing a hospital willing to host Kosilek.

The Boston Globe (http://b.globe.com/TJfHe0 ) reports that the names of the doctors were not made public.

Kosilek was named Robert when he killed his wife, Cheryl, in Mansfield in 1990.